[PATCH 3.16 177/328] x86/microcode/intel: Check microcode revision before updating sibling threads

[Ben Hutchings]

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ashok Raj <ashok.raj@xxxxxxxxx>

commit c182d2b7d0ca48e0d6ff16f7d883161238c447ed upstream.

After updating microcode on one of the threads of a core, the other
thread sibling automatically gets the update since the microcode
resources on a hyperthreaded core are shared between the two threads.

Check the microcode revision on the CPU before performing a microcode
update and thus save us the WRMSR 0x79 because it is a particularly
expensive operation.

[ Borislav: Massage changelog and coding style. ]

Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Tested-by: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: Arjan Van De Ven <arjan.van.de.ven@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1519352533-15992-2-git-send-email-ashok.raj@xxxxxxxxx
Link: https://lkml.kernel.org/r/20180228102846.13447-3-bp@xxxxxxxxx
[bwh: Backported to 3.16:
 - s/mc->/mc_intel->/
 - Return 0 in this case
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -155,6 +155,18 @@ int apply_microcode(int cpu)
 	if (get_matching_mc(mc_intel, cpu) == 0)
 		return 0;
 
+	/*
+	 * Save us the MSR write below - which is a particular expensive
+	 * operation - when the other hyperthread has updated the microcode
+	 * already.
+	 */
+	rev = intel_get_microcode_revision();
+	if (rev >= mc_intel->hdr.rev) {
+		uci->cpu_sig.rev = rev;
+		c->microcode = rev;
+		return 0;
+	}
+
 	/* write microcode via MSR 0x79 */
 	wrmsr(MSR_IA32_UCODE_WRITE,
 	      (unsigned long) mc_intel->bits,
--- a/arch/x86/kernel/cpu/microcode/intel_early.c
+++ b/arch/x86/kernel/cpu/microcode/intel_early.c
@@ -653,6 +653,17 @@ static int apply_microcode_early(struct
 	if (mc_intel == NULL)
 		return 0;
 
+	/*
+	 * Save us the MSR write below - which is a particular expensive
+	 * operation - when the other hyperthread has updated the microcode
+	 * already.
+	 */
+	rev = intel_get_microcode_revision();
+	if (rev >= mc_intel->hdr.rev) {
+		uci->cpu_sig.rev = rev;
+		return 0;
+	}
+
 	/* write microcode via MSR 0x79 */
 	native_wrmsr(MSR_IA32_UCODE_WRITE,
 	      (unsigned long) mc_intel->bits,